Method for the construction of vertical power transistors with differing powers by combination of pre-defined part pieces

ABSTRACT

A method for designing a first vertical MOS power transistor having a specified design power level. The method comprises the steps of composing a layout of the vertical MOS power transistor as a combination of at least partly differing layout part pieces, each of the part pieces having known design data, the part pieces including at least one first layout part piece comprising a given number of single transistor cells, and adjusting the specified design power level of the first vertical MOS power transistor by using the known design data of the part pieces and based on the layout combination of the part pieces.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/576,736, filed Jan. 16, 2008 and entitled “METHOD FOR THECONSTRUCTION OF VERTICAL POWER TRANSISTORS WITH DIFFERING POWERS BYCOMBINATION OF PRE-DEFINED PART PIECES,” which has been allowed and willissue as U.S. Pat. No. 8,190,415 on May 29, 2012, and which is theNational Phase Entry in the U.S. of PCT/DE2005/001780, filed Oct. 5,2005 and entitled “METHOD FOR THE CONSTRUCTION OF VERTICAL POWERTRANSISTORS WITH DIFFERING POWERS BY COMBINATION OF PRE-DEFINED PARTPIECES,” which claims priority to German Patent Application No. DE102004048278, filed Oct. 5, 2004 and entitled “Simulations—und/oderLayoutverfahren für Leistungstransistoren, die für unterschiedlicheLeistungen ausgelegt sind,” the entire disclosures of each of which arehereby incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a method for the construction of vertical powertransistors (DMOS or IGBT) having a variable channel width, which may bedrawn or designed by the designer so as to have the desired channelwidth and thus the appropriate on-resistance and which may be describedon the basis of electric parameter depending on the channel width. Inthe present case discrete and integrated vertical power transistors arecontemplated.

BACKGROUND OF THE INVENTION

A vertical transistor used in the field of power electronics typicallyconsists of a plurality of single transistor cells arranged in aparallel manner and a terminal contact for the gate electrode, as is forinstance described in U.S. Pat. No. 5,844,277, cf. FIGS. 2A to D andFIGS. 5-7, and U.S. Pat. No. 5,763,914. These single transistor cellshave a common gate electrode, a common drain terminal at the back sideof the silicon wafer and separate source or well terminals within thesilicon that, however, are connected in parallel by a common metalelectrode. The number and the size of the single transistor cellsdetermine the transistor area, the channel width and the on-resistance,as is described by Baliga in Power Semiconductor Devices, 1995, pages367 onwards. In order to obtain the desired on-resistance of a verticalDMOS transistor in conventional techniques the entire transistorincluding a corresponding active area and an edge structure connectableto the periphery has to designed. Starting from a transistor having afirst on-resistance to obtain a second transistor having a differingon-resistance it is necessary to newly design the entire transistor.Typically, the required electric parameters of the vertical DMOStransistor are measured and described separately for each differenttransistor.

For designing integrated circuits methods are known in which the circuitis composed by individual blocks. As e.g. shown in U.S. Pat. No.6,769,007, in which is described the composing of an integrated circuiton the basis of individual blocks. Also, the composing of an integratedcircuit or parts thereof on the basis of individual blocks separately tobe connected by metal conductors is described in U.S. Pat. No. 6,651,236and U.S. Pat. No. 6,591,408.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to provide a method that enables todesign vertical power transistors having differing on-resistances in asimplified manner.

According to one aspect of the present invention this object is solvedby a method for designing a vertical power transistor having a specifieddesign power, wherein the method comprises: composing a layout of thevertical MOS power transistor as a combination of at least partlydiffering layout part pieces, each having known design data, includingat least a first layout part piece that has a pre-determined number ofsingle transistor cells (2), and adjusting the specified design powerusing the known design data and the number of layout part pieces used.

Thus, according to the present invention the required time to be spentby the designer for the design of vertical power transistors having adefined active area may be reduced and also the effort for measurementsand the description may be reduced. The designer is provided with a“pre-design”, which may be appropriately adapted to the requirements ofthe designer in a fast and efficient manner. Furthermore, an efficientparametric description of the device may be achieved.

Due to the method according to the present invention transistors ofdifferent power, that is, different area or different on-resistance, maybe designed in an efficient manner, i.e., fast and cost effective. Theknown design data allows an efficient description of the designedtransistor on the basis of the initial pieces and appropriatecalculation techniques for obtaining individual transistor parametersfrom known parameters of the single pieces.

In a further embodiment the specified design or target power is adjustedby the number of the first part pieces. In this way the desired powermay be calculated and adjusted in an efficient manner.

In a further embodiment the single transistor cells of the first partpieces have the same configuration, thereby allowing the design ofstandard transistor configurations in an efficient manner.

In a further embodiment at least some of the part pieces comprise edgeportions that may be composed in a sectional manner so as to form acomplete edge portion in the layout of the vertical MOS powertransistor. In this way the design may be accomplished without any newtransistor components, such as adapted edge components.

In a further embodiment part pieces having identical edge portionscomprise a defined number of always identical single transistor cells inthe same geometrical arrangement, whereby the efficiency is furtherimproved.

In a further embodiment each part piece comprises a defined section ofthe complete edge portion. In this way a complete transistor structuremay be defined with a low number of design steps, since the edgeportions are already included in the individual part pieces.

In a further embodiment a second part piece is used that comprises atleast a gate terminal.

In a further embodiment the second part piece comprises a certain numberof identical single transistor cells.

In a further embodiment the second part piece comprises a section of thecomplete edge portion.

In a further embodiment a third part piece is provided that differs fromthe first and second part pieces in at least one design characteristic.In this manner a plurality of transistor structures having differingpower may be designed on the basis of only three different part pieces.

In a further embodiment the first, second and third part pieces comprisesections of the edge portion, which form the complete edge portion.

In a further embodiment the method comprises: designing at least asecond vertical power transistor having a second differing specifieddesign power by combining at least the first, second and third partpieces into device units of differently sized total area, wherein thescaling of the power between the vertical MOS power transistor and thesecond vertical MOS power transistor is determined by the size of a partpiece forming the central portion of device area. That is, if necessary,different transistor types may efficiently be designed on the basis of agiven power scaling, wherein no steps for the designing of new layoutobjects are required.

In a further embodiment each part piece is a standardized part piece, sothat the part pieces may be combined in any manner.

In a further embodiment each part piece comprises a layout adjusted tocorresponding dividing grid. In this way an efficient compilation may beachieved on a given platform, wherein the entirety of thecharacteristics is well-observable and efficiently computable due to thefixed layouts of the part pieces.

In a further embodiment at least one type of part pieces is provided,which does not comprise single transistor cells. Hence, the flexibilityof the method more further be enhanced.

In a further embodiment the at least one type of part pieces withoutsingle transistor cells comprises part pieces including edge portions.

In a further embodiment at least one part piece is provided that doesnot include an edge portion.

In a further embodiment at least one part piece is provided thatcomprises a bond pad layout.

In a further embodiment at least one part piece is provided thatcomprises a drain terminal layout and/or a source terminal layout.

In a further embodiment the method further comprises: creating at leastsome differing layout part pieces by dividing the complete layout of avertical power transistor having known design data. In this manner therequired program objects may be created in a highly flexible manner andmay be used for the further design operation of transistors, wherein inthis case the constructional specialities of the base layout are takeninto consideration in the new design process.

In a further embodiment the dividing comprises: creating a plurality ofdiffering types of part pieces, wherein part pieces of the same typehave the same configuration and the same design data; and calculatingthe design data of each type from the known design data of the completelayout in order to obtain standardized part pieces for a layout that isfixed to a dividing grid.

According to a further aspect the object is solved by a method forcreating standardized layout part pieces for designing vertical MOSpower transistors configured for differing power levels. The methodcomprises the steps of: creating at least some differing layout partpieces by dividing a complete layout into a plurality of singletransistor cells of a vertical MOS power transistor having known designdata; creating a plurality of differing types of part pieces, whereinpart pieces of a respective type have the same configuration and thesame design data; and calculating the design data of each type from theknown design data of the complete layout to obtain standardized partpieces for a layout fixed to a dividing grid.

In this manner respective design tools may efficiently and highlyflexibly be created.

In still a further aspect the object is solved by a system for designingvertical MOS power transistors that are configured for differing powerlevels. The system comprises a computer aided platform for the creationof layouts from layout part pieces according to a selected dividinggrid, wherein the layout determines the construction of the vertical MOSpower transistor; two or more differing part pieces, each of which has adifferent function and a different design data, wherein at least onefirst layout part piece including a certain number of identical singletransistor cells is provided, wherein the tow or more part pieces incombination with the at least one first part piece may be combined to acomplete vertical MOS power transistor, wherein the power levels of thelayouts of the vertical MOS power transistors are defined by the numberof first layout part pieces.

Further advantageous embodiments are provided in the claims and thefollowing detailed description.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will be described based on embodiments by referring to theschematic drawings, in which

FIG. 1 is a plan view of a vertical power transistor having a firstarea;

FIG. 2 depicts a vertical power transistor having a smaller areacompared to the area of FIG. 1;

FIG. 3 illustrates single pieces of a divided vertical power transistor;

FIG. 4 illustrates a vertical power transistor composed of single pieceswith an area as shown in FIG. 1;

FIG. 5 illustrates a vertical power transistor composed of single pieceswith a second area as shown in FIG. 2;

FIG. 6 shows a vertical power transistor divided into single piecesincluding a divided edge structure; and

FIG. 7 shows a vertical power transistor divided into single piecesincluding a piece that includes a bond pad opening.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 a transistor 1, that is, a layout corresponding to a specificvertical power transistor is shown. This layout is divided intodiffering part pieces as shown in FIG. 3, including: a first end piece5, which may also include a gate terminal 3, for example, a second endpiece 6 and a central or middle piece 7. Each of these part piecesincludes a certain number of single transistor cells 2 and acorresponding part piece of an edge structure 9, as is shown in FIG. 1.

In FIG. 4 a transistor 8 is shown, that is, the transistor's layout,which has the same area as the transistor 1, wherein the transistor 8 ofthis example is composed of the first end piece 5, the second end pieces6 and two central pieces 7. The parameters of the composed transistormay now be calculated on the basis of the parameters of the individualpieces.

The area of the transistor 8 is the sum of the area of the two endpieces 5 and 6 and two times the area of the central piece 7. Byinserting further central pieces 7 the area of the transistor may nearlyarbitrarily be increased. The area of the composed transistor havingcentral pieces of number x may be described by:A _(transistor) =A _(end piece5) +A _(end piece6) +x*A _(central piece7)

In the same way the capacitance of the composed transistor 8 may bedetermined. The capacitance of the composed transistor may be described,when using the well-known formula of the parallel connection ofcapacitors, by:C _(transistor) =C _(end piece5) +C _(end piece6) +x*C _(central piece7)

As derivable from the well-known formula of the parallel connection ofresistors the resistance of the transistor composed of an end piece 5,an end piece 6 and central pieces of number x may written as:1/R _(transistor)=1/R _(end piece5)1/R _(end piece6) +x*1/R_(central piece7)

In this example, the size of the central piece 7 determines the stepwidth of the available area grading, that is, when using large centralpieces 7 a coarse grading of the areas may be obtained. When using smallcentral pieces 7, however, a finer grading of the areas may begenerated. The size of the single transistor cell determines the minimumpossible size of the central piece 7.

If a transistor is to be designed that corresponds, for example, to thetransistor 4, that is, the layout of FIG. 2, this may be accomplished bycomposing the two end pieces 5 and 6. This also represents the smallestpossible area, when a given type of central pieces 7 is provided. Othercentral pieces may also be used so as to enhance the design flexibility.

FIG. 6 illustrates further possibilities or embodiments for the use orthe creation of different types of layout part pieces, which may be usedas initial objects during the design process in order to establish thedesired transistor structure in the form of a layout. For example, theedge structure may also be divided into single pieces. In this case thepartitioned transistor consists of an end piece 11 possibly including agate terminal 3, a central piece 12 comprising a defined number ofsingle transistor cells 2, a part piece of the edge structure 13 formingthe corners based on a rotated or mirrored configuration, and an edgepiece 14.

FIG. 7 depicts a piece of a partitioned transistor 15, that is, of itslayout that includes a further structure. In the present example a bondpad opening 16 is provided as may be used in discrete power transistors.In other embodiments any other structures may be used, such as drain orsource terminals of integrated power transistors.

The part pieces shown in the figures thus represent efficient designtools that may be created and/or compiled in a computer aided platform(not shown) according to the principles discussed above in order togenerate a plurality of differing transistor designs.

One advantageous embodiment comprises a method for the construction ofvertical metal oxide semiconductor (MOS) power transistors that areadapted to different power levels. The method comprises that thesetransistors are composed to a complete device design as a combination ofdiffering standardized part pieces, each of which corresponds to aspecified function and has a corresponding layout based on a dividinggrid and also has known data. Thus, a part piece, such as the part piece7, includes a defined number of identical single transistor cells 2 inthe same geometrical arrangement together with a certain edge portion 9,another part piece, such as the part piece 5, includes a certain numberof identical transistor cells 2 together with the gate terminal 3 andanother section of the edge portion, and a further part piece, such asthe part piece 6, includes a certain number of identical transistorcells 2 together with a further section of the edge portion, and thesepart pieces are combined to form device units of differing total area,wherein the power grading results from the size of the part pieceforming the centre of the device area.

One advantageous embodiment comprises a method for the construction ofvertical MOS power transistors that are adapted to different powerlevels, wherein the method comprises that these transistors are composedto a complete device design as a combination of differing standardizedpart pieces, each of which corresponds to a specified function and has acorresponding layout based on a dividing grid and also has known data.Thus, a first part piece, such as the part piece 12, includes a definednumber of identical single transistor cells 2 in the same geometricalarrangement, a second part piece, such as the part piece 11, includes acertain number of identical transistor cells 2 together with the gateterminal 3, and a third part piece, such as the part piece 15, includesopen bond pads 16, and wherein further part pieces are provided thatform certain sections of the edge portion, such as the portions 13, 13a, 14, and wherein the part pieces are combined to device units ofdiffering total area, wherein the power grading results from the size ofthe part piece forming the centre of the device area, such as the partpiece 12.

In a further embodiment the device does not comprise the third partpiece, such as the part pieces 15.

In a further embodiment the third part piece may also comprisefunctional elements other than the bond pads 16.

What is claimed is:
 1. A computer-aided method of designing a verticalmetal oxide semiconductor power transistor having a specifiedon-resistance, the method comprising: computer-aided composing acomplete layout of the vertical metal oxide semiconductor powertransistor as a combination of at least partly differing layout partpieces, said part pieces defining the layout of the vertical metal oxidesemiconductor power transistor, each part piece having known design dataand known electrical parameters, wherein at least some of said partpieces are first layout part pieces, and each first layout part piece atleast contains a plurality of single transistor cells and an edgeportion; computer-aided adjusting the specified on-resistance byadjusting the number of said first layout part pieces used in the layoutof the vertical metal oxide semiconductor power transistor; and whereinfirst part pieces having the same edge portion include a specifiednumber of identical single transistor cells having the same geometricalarrangement.
 2. A computer-aided method of designing a vertical metaloxide semiconductor power transistor having a specified on-resistance,the method comprising: computer-aided composing a complete layout of thevertical metal oxide semiconductor power transistor as a combination ofat least partly differing layout part pieces, said part pieces definingthe layout of the vertical metal oxide semiconductor power transistor,each part piece having known design data and known electricalparameters, wherein at least some of said part pieces are first layoutpart pieces, and each first layout part piece at least contains aplurality of single transistor cells and an edge portion; computer-aidedadjusting the specified on-resistance by adjusting the number of saidfirst layout part pieces used in the layout of the vertical metal oxidesemiconductor power transistor; and wherein each first layout part piecehas the same configuration and has identical design data.
 3. Acomputer-aided method for designing a vertical metal oxide semiconductorpower transistor having a specified on-resistance, the methodcomprising: computer-aided composing a complete layout of the verticalmetal oxide semiconductor power transistor as a combination of at leastpartly differing layout part pieces, said part pieces defining thelayout of the vertical metal oxide semiconductor power transistor, eachpart piece having known design data and known electrical parameters,wherein at least some of said part pieces are first layout part pieces,and each first layout part piece containing at least a plurality ofsingle transistor cells, wherein part pieces having same edge portionsinclude a specified number of identical single transistor cells havingthe same geometrical arrangement; and computer-aided providing thespecified on-resistance of the layout by adjusting the number of saidfirst layout part pieces assembled in the layout of the vertical metaloxide semiconductor power transistor.
 4. The method of claim 3, whereineach said first part piece contains an edge portion.
 5. A system fordesigning vertical metal oxide semiconductor power transistors havingdifferent on-resistances or design power levels, comprising: a processorcoupled with a memory; said memory comprising code executable by theprocessor, said code configured, when executed, to implement a designtool for designing vertical metal oxide semiconductor power transistorsby: generating a layout from layout part pieces according to a grid,said generated layout defining the construction of a vertical metaloxide semiconductor power transistor, said layout part pieces definingthe structure of the vertical metal oxide semiconductor powertransistor; said layout part pieces belong to the design tool andcomprise two or more differing part pieces having different functionsand corresponding design data, wherein first layout part pieces having aspecified number of identical single transistor cells are provided andother part pieces are provided for combination with said first layoutpart pieces into the layout of a complete power transistor and whereinan on-resistance or a design power level of the layout of the verticalmetal oxide semiconductor power transistor is defined by the number ofsaid first layout part pieces; and wherein each said first layout partpiece has the same configuration and has identical design data.
 6. Thesystem of claim 5, wherein each said first layout part piece contains anedge portion.
 7. The system of claim 5, wherein part pieces having thesame edge portion include a specified number of identical singletransistor cells having the same geometrical arrangement.